Controlling air movers based on acoustic signature

ABSTRACT

In a system that employs multiple air movers (e.g., fans) within an enclosure, the air movers are controlled in an attempt to optimize cooling efficiency of the system. In some aspects, current cooling efficiency is indicated based on one or more characteristics of an acoustic signature in the enclosure. In particular, a reduction in cooling efficiency may be indicated by spreading of an acoustic peak of the acoustic signature. Accordingly, improved cooling efficiency may be achieved by controlling the air movers in a manner that reduces spreading of such an acoustic peak.

CLAIM OF PRIORITY

This application claims the benefit of and priority to commonly owned U.S. Provisional Patent Application No. 61/522,696, filed Aug. 12, 2011, the disclosure of which is hereby incorporated by reference herein.

BACKGROUND

Some computing systems enclosures employ multiple air movers (e.g., fans) to provide air flow cooling for the system. For example, a typical personal computer includes a power supply fan, one or more processor fans, and an exhaust fan. As another example, a server system typically includes one or more fans for each rack of the server system.

In such systems, the control setting for a given fan is commonly selected based on a temperature measurement associated with that fan. For example, the operating speed of a fan associated with a processor is generally controlled based on the temperature at that processor. As another example, the operating speed of an exhaust fan is generally controlled based on air temperature readings within the enclosure or, in some cases, on inlet ambient air temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

Sample features, aspects and advantages of the disclosure are described in the detailed description and appended claims that follow and the accompanying drawings, wherein:

FIG. 1 is a simplified diagram of an embodiment of a system including an apparatus for controlling fans in accordance with the teachings herein;

FIG. 2 is a flowchart of an embodiment of operations for controlling fans in accordance with the teachings herein;

FIG. 3 is a simplified diagram that illustrates sample fan interactions and an embodiment of an apparatus for controlling fans in accordance with the teachings herein;

FIGS. 4A and 4B are simplified graphs illustrating a theoretical example of an effect that fan interaction has on an acoustic signature;

FIG. 5 is a flowchart of an embodiment of operations for reducing spreading of an acoustic peak of a frequency spectrum in accordance with the teachings herein;

FIG. 6 is a flowchart of an embodiment of operations for controlling fans based on signals from multiple transducers in accordance with the teachings herein;

FIG. 7 is a simplified block diagram of an embodiment of a system employing an optimization algorithm for controlling fans in accordance with the teachings herein;

FIG. 8 is a simplified diagram of an embodiment of a system including a housing for multiple fans; and

FIG. 9 is a simplified diagram of an embodiment of a server system including multiple fans.

In accordance with common practice, the various features illustrated in the drawings are typically not drawn to scale. Accordingly, the dimensions of the various features are arbitrarily expanded or reduced for clarity in some cases. In addition, the drawings are typically simplified for clarity. Thus, the drawings will generally not depict all of the components of a given apparatus or method. Finally, like reference numerals are used to denote like features throughout the specification and figures.

DETAILED DESCRIPTION

The disclosure relates in some aspects to controlling multiple air movers in a manner that improves cooling efficiency of a system. In general, cooling efficiency tends to be higher when there are minimal interactions between the air movers since the air movers support a more balanced air flow in this case. For example, a more balanced air flow will occur when air flows from different air movers are substantially in phase and, hence, constructive. In contrast, cooling efficiency tends to be lower when undesirable interactions between the air movers result in less balanced air flow in the system. For example, unbalanced air flow will occur when air flows from different air movers are out of phase and, hence, destructive. In some embodiments, these different conditions are identified by using one or more transducers to acquire spectral information associated with air flow in an enclosure. Here, a more narrowband acoustic spectrum is expected when there is minimal interaction between the air movers, while a wider acoustic spectrum is expected when there is more air mover interaction. Thus, cooling efficiency may be improved in such a system by controlling the air movers in a manner that results in a narrower acoustic spectrum. For purposes of illustration, several embodiments are described below in the context of a fan control system. It should be appreciated, however, that the teachings herein may be applicable to other types of air movers as well.

FIG. 1 illustrates an embodiment of a control circuit 102 for controlling several fans 104 in an enclosure 106. In a typical implementation, the enclosure 106 comprises a housing for a computing system as discussed in more detail below. The control circuit 102 receives transducer signals 108 from one or more transducers 110 and processes these signals to generate control signals 112 that control the fans 104.

The transducer signals 108 are representative of acoustic signatures in the enclosure 106. For example, in some embodiments, each transducer 106 comprises a microphone that detects sound such as fan noise within the enclosure 106. The signals generated by the microphone are thus representative of one or more characteristics of the sound in the enclosure 106. Such a characteristic may comprise a frequency spectrum, an amplitude spectrum, or some other acoustic-related quality.

Different fan operating conditions will result in different acoustic signatures in the enclosure 106. In particular, the acoustic signature generally changes when the loading on a fan changes (e.g., when there is a change in the rotational speed and/or air flow of one or more of the fans 104). For example, a frequency spectrum associated with noise from a given fan will generally have a peak corresponding to the blade passing frequency of the fan and smaller peaks corresponding to harmonics of the blade passing frequency. As the rotational speed of the fan changes, a corresponding shift occurs in the blade passing frequency which results in a shift in the locations of the peaks in the frequency spectrum.

In accordance with the teachings herein, the control circuit 102 controls the fans 104 to reduce spreading of at least one acoustic peak of an acoustic signature represented by the transducer signals 108. For example, air flow generated by a first fan 104 will interact with (e.g., affect the loading on) a second fan 104 under certain conditions. This fan interaction is undesirable in cases where it causes the fans to work against one another rather than with one another to move air through the system. However, such an undesirable fan interaction may be evidenced by spreading of one or more acoustic peaks in an acoustic signature generated under these conditions. Such spreading is caused, for example, by modulation of the loading on a given fan as a result of the fan interaction. In such a case, as the rotational speed and/or air flow of the fan shifts over time (e.g., within a certain range) due to the loading modulation, the acoustic peaks of the corresponding frequency spectrum will spread by a corresponding amount.

Accordingly, the control circuit 102 generates the control signals 112 in a manner that tends to reduce this spreading. For example, by controlling one or more of the frequency, voltage, or phase of the control signals, the operating point (e.g., rotational speed and/or phase) of one or more of the fans 104 is adjusted to reduce the undesirable fan interactions. By subsequently analyzing the peak spread of a later acquired acoustic signature, the control circuit 102 can determine whether the adjustment of the control signals did in fact reduce the fan interactions. Through the use of this scheme, the control circuit 102 controls the fans 104 so that they more effectively work together to move air through the system. Thus, cooling efficiency in the system may be improved since the fans 104 may use less power to provide the desired level of cooling. In addition, fan-related noise in the system may be reduced in some cases due to more efficient fan operation.

Advantageously, the fan control scheme of FIG. 1 can dynamically adapt to changes that affect air flow in the system over time. For example, optimum air flow in a system is generally a function of one or more factors including fan speed, physical orientation of the fans, the design of the system enclosure, air filters, screens, or fan impeller/housing design. In the event there is a change in any of these factors that adversely affects the aerodynamics in the enclosure 106, this change is automatically detected (e.g., by detecting spreading of an acoustic peak) and then compensated for by adjusting fan control signals as taught herein. For example, in a system that includes general purpose and graphics processors, the loading on different processor fans will be different and will change over time due to changes in the temperatures of the processors. Since the fan control scheme of FIG. 1 is able to detect and respond to these types of changes, this fan control scheme may provide better cooling efficiency as compared to a system where the fan control settings are fixed for a specific system configuration, system impedance, and speed range.

Furthermore, the fan control scheme of FIG. 1 provides a relatively straightforward way of accounting for the complex system enclosure impedance, air flow impedance, and air flow interaction that result from the use of multiple fans. Accordingly, the fan control scheme of FIG. 1 may provide better cooling efficiency as compared to a system where each fan is independently controlled.

The control circuit 102 optionally generates the control signals 112 based on signals 118 received from one or more transducers 120. As discussed in more detail below, in some implementations, the control signals are generated based on one or more of: inlet ambient air temperature, temperature in the enclosure, rotational speed of one or more of the fans 104, power supplied to one or more of the fans 104, current supplied to one or more of the fans 104, or voltage supplied to one or more of the fans 104. Accordingly, each transducer 120 will be of a suitable type to provide the desired information. In an implementation that employs more than one transducer 120, two or more of the transducers 120 may be of the same type or different types.

The components of FIG. 1 may be implemented in various ways in different embodiments. For example, the control circuit 102 may be implemented in an integrated circuit (e.g., an application specific integrated circuit (ASIC)) configured to provide the desired functionality, a processor (e.g., a digital signal processor (DSP) or general purpose processor) that executes code to provide the desired functionality, a state machine, analog circuitry, some other suitable circuitry, or some combination of the above. The processing of the received signals 108 to provide the control signals 112 may thus be performed in the digital domain (e.g., a DSP configured to perform a fast Fourier transform (FFT) function) and/or in the analog domain (e.g., an analog circuit configured to perform an FFT function).

In the example of FIG. 1, the transducer signals 108 are received via a receiver circuit 114 and passed to the control circuit 102, and the signals 118 are received via a receiver circuit 122 and passed to the control circuit 102. The circuitry used here depends on the technology employed in a given implementation. In an implementation where a transducer 110 or 120 outputs analog signals, a receiver circuit 114 or 122 includes, for example, a buffer, discrete transistors, an amplifier (e.g., an OP amp), or other suitable circuitry for receiving analog signals. In an implementation where a transducer 110 or 120 outputs digital signals, a receiver circuit 114 or 122 includes, for example, a digital buffer, discrete transistors, a latch, or other suitable circuitry for receiving digital signals. Here, it should be appreciated that each receiver circuit 114 or 122 will include separate receiver components that are coupled to dedicated transducer signal paths (e.g., discrete wires or printed circuit board (PCB) traces) in cases where the receiver circuit 114 or 122 is coupled to multiple transducers 110 or 120.

Also in the example of FIG. 1, a driver circuit 116 drives the control signals 112 based on signals output by the control circuit 102. The circuitry used for the driver circuit 116 depends on the technology employed in a given implementation. In an implementation where the control circuit 102 outputs digital signals, the driver circuit 116 includes, for example, a digital buffer, discrete transistors, a latch, or other suitable circuitry for receiving digital signals. In an implementation where the control circuit 102 outputs analog signals, the driver circuit 116 includes, for example, a buffer, discrete transistors, an amplifier (e.g., an OP amp), or other suitable circuitry for receiving analog signals.

The driver circuit 116 also includes circuitry for outputting the control signals in an appropriate format for controlling the fans 104. For example, a DC fan is typically controlled by a pulse width modulation (PWM) signal. Hence, the driver circuit 116 will be configured to output an appropriate PWM signal in this case. Conversely, an AC fan is typically controlled by a variable frequency AC signal. Thus, the driver circuit 116 (e.g., employing a variable frequency inverter) will be configured to output an appropriate variable frequency signal in this case. It should be appreciated that the driver circuit 116 typically includes separate driver components that are coupled to dedicated signal paths so that each of the fans 104 is controlled in an independent manner.

In some implementations, one or more of the circuits 114, 116, or 122 are configured to convert signals from one domain to another. For example, in some cases, a receiver circuit 114 or 122 includes analog-to-digital conversion circuitry to convert analog signals from a transducer 110 or 120 to digital signals used by the control circuit 102. In addition, in some cases, the driver circuit 116 includes digital-to-analog conversion circuitry to convert digital signals from the control circuit 102 to analog signals that drive the fans 104.

The control circuit 102, the receiver circuit 114, the driver circuit 116, and the receiver circuit 122 may be implemented separately or within a common apparatus. For example, in various embodiments, these circuits may be implemented within a single integrated circuit, implemented on a single PCB, or implemented as discrete components.

In some implementations, each transducer 110 comprises an acoustic transducer (e.g., a microphone) that is capable of detecting mechanical waves in air or other similar medium. In other implementations, each transducer 110 comprises or is based on a static or dynamic pressure transducer.

A transducer 120 will take different forms depending on the physical property being measured. In an implementation where the signals 118 are representative of temperature, a transducer 120 comprises a temperature sensor or some other type of transducer that is capable of generating signals from which temperature-related information may be derived. In an implementation where the signals 118 are representative of rotational speed of one or more of the fans 104, a transducer 120 comprises a Hall sensor or some other type of transducer that is capable of generating signals from which fan rotation information may be derived. In an implementation where the signals 118 are representative of power, current, or voltage supplied to one or more of the fans 104, a transducer 120 comprises a power sensor, a current sensor, a voltage sensor, or some other type of transducer that is capable of generating signals from which this information may be derived. In an implementation where the signals 118 are representative of mechanical vibration, a transducer 120 generates signals from which mechanical vibration-related information may be derived.

To reduce the complexity of FIG. 1, the fans 104, the transducer(s) 110, and the transducer(s) 120 are each represented by a single box. In practice, the fans 104 are located at different locations (e.g., adjacent different processors, exhaust vents, inlet vents, etc.) to provide air flow at designated locations within the enclosure 106. Similarly, in an implementation that uses multiple transducers 110, these transducers are typically located at different locations to acquire acoustic information from different places within the enclosure 106. Also, in an implementation that uses multiple transducers 120, these transducers are typically located at different locations to acquire information from different places within the enclosure 106.

In general, a control circuit will include or have access to one or more memory storage components for storing one or more of: data, parameters, executable code, or some other type of information that is used in conjunction with fan control operations. For example, in FIG. 1, the control circuit 102 includes a memory device 124.

FIG. 2 describes a sample embodiment of high-level operations for controlling fans in accordance with the teachings herein. This flowchart describes operations that are typically performed on a repeated basis (e.g., periodically or continually) in an attempt to maintain optimum air flow within an enclosure under dynamic operating conditions. It should be appreciated, however, that these operations also could be employed on a static basis to provide long-term fan control settings. The operations of FIG. 2 (or any other operations discussed herein) may be performed by the components of FIG. 1 or by other suitable components. Also, one or more of the operations described herein may not be employed in a given implementation.

As represented by block 202, at some point in time, signals representative of an acoustic signature due to interaction of fans in an enclosure are received. In a typical implementation, these received signals were generated by one or more acoustic transducers (e.g., a microphone), each of which is located within the enclosure or in the vicinity of the enclosure (e.g., adjacent an inlet vent or an outlet vent).

As discussed above, the received signals will be analog or digital signals depending on the particular transducer implementation. In some cases, analog signals from a transducer are sampled (e.g., on a periodic or continual basis) by a receiver circuit and provided to a digital control circuit. In some cases, analog signals from a transducer are provided on a continual basis to an analog control circuit via an analog receiver circuit. In some cases, digital signals from a transducer simply forwarded to a digital control circuit via a digital receiver circuit.

As represented by block 204, control signals are generated (e.g., adjusted) based on the signals received at block 202. In particular, the control signals are generated in a manner that controls the fans to reduce the spreading of at least one acoustic peak of the acoustic signature. For example, upon analyzing the received signals, it may be determined that spreading of an acoustic peak has increased relative to spreading identified by a prior analysis or it may be determined that the spreading of an acoustic peak exceeds a defined spreading value (e.g., a designated maximum, a designated range, or some other type of target value). In such a case, the control signal for one or more of the fans is adjusted (e.g., by changing the frequency and/or phase of the signal) in a manner that is expected to decrease undesirable fan interaction and, hence, decrease the spreading of the acoustic peak. A more detailed example of the operations of block 204 is described below in conjunction with FIG. 5.

As represented by block 206, the fans are driven using the generated control signals. Typically, different control signals are used to control different fans. In some implementations, however, a single control signal is used to control a subset of the fans.

The manner in which a control signal is controlled to change the speed of a fan depends of the type of fans being used. For example, in some implementations, a DC fan is driven via a PWM signal. Here, the speed of the DC fan is controlled by changing the width of the pulse output by a driver circuit. As another example, in some implementations, an AC fan is driven via a variable frequency AC signal. In this case, the speed of the AC fan is controlled by changing the frequency (at a motor-specific volts/hertz ratio) of the AC signal output by a driver circuit (e.g., based on a control signal from a control circuit).

The relative phase of two or more fans is controlled, for example, by temporarily (e.g., instantaneously) changing the speed of one or more of the fans. Thus, for PWM-based DC fans, the relative phase of the fans is changed by temporarily adjusting the pulse width for at least one of the fans. For AC fans, the relative phase of the fans is changed by temporarily adjusting the frequency of the AC signal for at least one of the fans.

The arrow from block 206 to block 202 indicates that the operations of FIG. 2 are typically repeated to dynamically adjust the control signals over time. Thus, a series of other signals (e.g., in the form of a continuous signal) representative of other acoustic signatures due to other interactions of the fans are received over time (block 202) and at least one of the control signals is adjusted over time based on the received other signals (block 204). In this way, optimum cooling within the enclosure may be achieved even under dynamic fan loading conditions due to, for example, changes in processor workload.

As described in more detail below in conjunction with FIG. 7, in some implementations, the fan control signals are repeatedly adjusted based on an optimization algorithm. For example, such an algorithm may employ a brute force scheme, a lookup table-based scheme, a least mean square-based scheme, or some other suitable scheme that attempts to keep the spreading to a minimum.

FIG. 3 illustrates, in a simplified manner, sample fan interactions that affect spreading of acoustic peaks of an acoustic signature. In this example, an enclosure 302 for a computing system is shown as housing a PCB 304, (e.g., including processors, memory devices, and other integrated circuits, not shown), and fans 306, 308, 310, and 312. To reduce the complexity of FIG. 3, other components such as power supplies, hard drives, interface circuits, and so on, that may be housed within the enclosure 302 are not shown.

The fans 306, 308, 310, and 312 are installed at designated locations within the enclosure 302 to provide certain cooling functions. The fan 306 is positioned adjacent an inlet duct (not shown) to draw outside air into the enclosure 302. The fan 308 is positioned adjacent an outlet duct (not shown) to exhaust air from the enclosure 302. The fans 310 and 312 are positioned over respective integrated circuits (e.g., processors, not shown) mounted on the PCB 304 to draw heat away from these integrated circuits.

The dashed arrows in FIG. 3 illustrate simplified air flows that are induced by the operation of the fans 306, 308, 310, and 312. As represented, for example, by the dashed arrows 314, 316, 318, and 320, the air flows induced by different fans interact with one another in different ways throughout the enclosure 302. In particular, the air flows will work with one another or against one another at various locations in the enclosure 302 depending on the current frequency and phase of the fans.

Moreover, as represented in a simplified manner by the dashed arrows 322, 324, and 326, these air flow interactions affect the operations of the fans under certain conditions. Specifically, the loading (i.e. static pressure vs. volume air flow) on a given fan, and hence the rotational speed of the fan, continually changes as a result of the air flow interactions. For example, an instantaneous merging of air flows in the same direction (in phase) will result in an instantaneous change of a combination of air flow and static pressure. If this air flow is directed toward an inlet or outlet of a fan (e.g., the fan 308), the loading on the fan will change and result in an instantaneous change (increase or decrease) in the fan speed. As another example, an instantaneous merging of air flows in opposite directions (out of phase) will result in an instantaneous change in air flow (e.g., a null in some case). For example, if this occurs near an inlet or an outlet of a fan (e.g., the fan 308), the loading on the fan could change and result in an instantaneous change in the fan speed.

Such fan interaction may be particularly prevalent in enclosures for computing systems which tend to be relatively small (e.g., much smaller than a building), yet have relatively stringent air flow requirements. For example, enclosures for computer graphics cards, personal computers, computer servers, and the like will typically each have several fans that move relatively large amounts of air to ensure that the electronic components in the enclosures are protected from overheating.

Once the air flow interactions within the enclosure 302 achieve a steady state, the loading on a given fan in the enclosure 302 may be modulated by these air flow interactions. That is, due to the complex nature of the air flow interactions, the loading on the fan will change within a given range in a repetitive manner over time. Hence, a modulation of the rotational speed of the fan is induced by the interaction of the air flows with the fan.

The modulation of a given fan results in a corresponding modulation of the blade passing frequency of the fan. The blade passing frequency is defined as the number of times a fan blade passes a fan support (e.g., fan strut) in a given period of time (e.g., one minute). Thus, the blade passing frequency is calculated based on the current rotational speed of the fan, the number of fan blades, and the number of fan supports (typically three or four). As described in more detail below at FIG. 4, a portion of the noise spectrum generated by a fan corresponds to the blade passing frequency and harmonics of the blade passing frequency. In some aspects, this is due to the mechanical action of the fan blades impacting the air and the moving air in turn hitting the fan supports.

In the example of FIG. 3, modulation of the fans 306, 308, 310, and 312 is detected by a microphone 328 that is coupled to a fan controller 330 (e.g., comprising receiver, control, and driver circuits embodied in an integrated circuit). As represented in a simplified manner by the curved dashed lines 332, 334, 336, and 338 in FIG. 3, each of the fans 306, 308, 310, and 312 generates noise that is detectable by the microphone 328. As discussed above, the noise from a given fan includes components corresponding to the blade passing frequency of that fan. Moreover, under certain conditions, these blade passing frequency components will be modulated due to the interactions of the fans 306, 308, 310, and 312 as discussed herein.

Hence, the fan controller 330 can use received signals from the microphone 328 to detect spreading of these frequency components that result from an increase in fan modulation caused by interactions between two or more of the fans 306, 308, 310, and 312. The fan controller 330 then changes the rotational speed and/or phase of one or more of the fans 306, 308, 310, and 312 to reduce this modulation and thereby potentially improve the cooling efficiency of the system.

FIGS. 4A and 4B depict an example of how such fan modulation affects the acoustic signature associated with the fan. A waveform 402 in FIG. 4A illustrates, in a simplified manner, an example of an acoustic signature associated with a fan that is operating without interactions with other fans. For example, the waveform 402 could correspond to the acoustic signature when the fan is operating in free space for a given static pressure and airflow. In contrast, a waveform 404 in FIG. 4B illustrates a simplified example of an acoustic signature associated with fan operation when there are undesirable interactions with at least one other fan in an enclosure.

The waveform 402 includes several peaks associated with the blade passing frequency of the fan. The leftmost and highest peak 406 corresponds to the fundamental blade passing frequency of the fan. The other major peaks correspond to harmonics of the blade passing frequency. Of note, in the absence of fan interaction, the peaks of the waveform are relatively “tonal” in nature. That is, each of the peaks (including peak 406) is associated with a relatively narrow frequency range.

In contrast, the peaks of the waveform 404 exhibit spreading due to modulation of the fan caused by the interactions between the fans in the enclosure. That is, as mentioned above, the fan interactions cause each peak associated with the blade passing frequency to shift slightly over time. As noted above, this frequency shifting will tend to stay within a small frequency range once the system achieves a steady state. Hence, the acoustic signature exhibits spreading of each acoustic peak as shown in the waveform 404 when there are undesirable interactions between the fans in the enclosure. For example, a relatively wide peak spread 408 is associated with the fundamental blade passing frequency in this case.

The peak spread may be defined in various ways. In some implementations, the peak spread is defined as the range of frequencies associated with specified dB points of a peak. For example, the specified dB points may correspond to the points on each side of the peak that are the specified number of dB (e.g., 3 dB) down in magnitude from the maximum magnitude of the peak. In the example of FIG. 4, this magnitude is expressed in terms of acoustic power. Sound pressure or sound pressure level (SPL) are alternative measures of this magnitude.

Based on the teachings herein, it should be understood that other mechanisms may be employed for optimizing cooling based on acoustic information from a fan enclosure. For example, in addition to noise components such as fan blade passing noise (e.g., caused by fan blades impacting the air), an acoustic signature (e.g., collected over a defined period of time) also may include noise that results from interactions of air flows generated by the fans. Accordingly, any changes (e.g., spreading) that occur relating to this noise may be monitored to determine whether and/or how to adjust the control signals for the fans.

With the above in mind, sample operations for adjusting fan control signals will be described in more detail with reference to the flowcharts of FIGS. 5 and 6. FIG. 5 illustrates an example of operations for identifying peak spread and adjusting control signals accordingly. FIG. 6 illustrates an example of operations for adjusting control signals based on signals received from different types of transducers.

Referring initially to FIG. 5, as represented by block 502, signals are received from one or more transducers. As discussed above in conjunction with block 202 of FIG. 2, these signals are representative of an acoustic signature in an enclosure. In an implementation where the control processing is implemented in the digital domain, the operations of block 502 involve, for example, sampling signals received from one or more microphones to generate a data set that includes data representative of the acoustic signature.

As represented by block 504, frequency spectrum information is generated based on the received signals. For example, the control processing may employ an FFT algorithm that operates on the received signals (e.g., a digital data set or analog signals) to extract frequency components of those signals. Accordingly, a frequency spectrum representative of the acoustic signature is obtained.

As represented by block 506, the spread of at least one peak of the frequency spectrum is identified. Here, the peaks indicated by the frequency spectrum information correspond to the acoustic peaks of the acoustic signature discussed above. In some implementations, identifying a peak spread from the frequency spectrum information involves determining the frequency range associated with the 3 dB points for the fundamental blade passing frequency and/or some other specified frequency (e.g., a harmonic of the blade passing frequency). Other techniques for determining a peak spread may be employed in other cases.

As represented by block 508, a determination is made as to whether the peak spread identified at block 506 needs to be reduced. In some implementations, this involves comparing the current peak spread value with a prior peak spread value (e.g., identified and stored during the last iteration of the algorithm). If the peak spread has increased, a decision may be made to reduce the peak spread.

In some implementations, the determination of block 508 involves comparing the current peak spread value with a target peak spread. If the peak spread is not within (e.g., less than or equal to) the target peak spread, a decision may be made to reduce the peak spread. Such a target value is determined, for example, based on simulations and/or empirical testing. The resulting value is then stored in a memory device that is accessible by the control processing (e.g., the memory device 124 in the control circuit 102 of FIG. 1).

As represented by block 510, based on the determination of block 508, at least one of the fan control signals is adjusted to reduce the peak spread, if applicable. A determination regarding which control signals are to be adjusted and how those control signals are to be adjusted may be made in various ways.

In some implementations, this determination is based on simulations and/or empirical testing. For example, it may be determined by such testing that adjusting the relative frequency and/or phase of certain fans in the enclosure tends to reduce spreading. As another example, it may be determined that different fans should be adjusted under different conditions (e.g., different loading conditions, different temperature conditions, and so on).

In some implementations, an iterative process is used to determine how to adjust the fan control signals. For example, upon determining that a peak spread is to be reduced, the control signal for one or more fans is adjusted in a defined manner (e.g., to increase fan frequency). The operations of blocks 502-508 are then repeated to determine whether this adjustment resulted in an increase or a decrease in the peak spread. If the peak spread decreased, the fan control signals are adjusted in the same manner as the immediately prior adjustment. If the peak spread increased, the fan control signals are adjusted in the opposite manner as the immediately prior adjustment, or are adjusted in some other manner. In an iterative process, the determination as to which control signals are to be changed and how those signals are to be changed (e.g., under certain conditions) may be specified, for example, by random selection, simulations, or empirical testing.

The arrow from block 510 to block 502 indicates that the operations of FIG. 5 are typically repeated to dynamically adjust the control signals over time. Thus, the peak spread is repeatedly checked over time to determine whether at least one of the control signals is to be adjusted.

As mentioned above, the teachings herein may be employed in embodiments that use different types of transducers (e.g., not just acoustic transducers). Referring now to FIG. 6, as represented by blocks 602 and 604, signals are received from different types of transducers in this scenario. For example, the signals received at block 602 correspond to acoustic-based signals (e.g., corresponding to block 502 of FIG. 5), while the signals received at block 604 are received from one or more transducers that provide information regarding other operating conditions in the enclosure.

In a typical implementation, temperature information is received via a temperature transducer (e.g., a temperature sensor) that provides signals indicative of temperature at a certain location in the enclosure. This temperature information is used, for example, to ensure that each of the fans is operating at a sufficient speed to achieve the desired cooling at the location of the temperature transducer (e.g., at a processor).

In some implementations, fan speed information is received from at least one transducer that detects the rotational speed of a fan and generates signals that are indicative of this rotational speed. In some cases, this type of transducer consists of a fan speed sensor such as a Hall sensor that is built into the fan. In other cases, a fan speed sensor is located external to a fan. The fan speed information is used, for example, to identify the fans being modulated (e.g., as indicated by repetitive changes in the fan speed) and to detect the extent of this modulation. Thus, this information is used in some cases to determine which control signals are to be adjusted and how these control signals are to be adjusted.

In some implementations, fan power-related information is received from at least one transducer that detects one or more of power, current, or voltage being supplied to a fan and that generates signals indicative of each detected parameter. In a typical case, this type of transducer consists of a power, current, or voltage sensor that is placed in-line with the fan control signals. The fan information is used, for example, to identify the fans being modulated (e.g., as indicated by minute changes in the fan loading, current draw, or applied voltage) and to detect the extent of this modulation. Thus, this information can be used to determine which control signals are to be adjusted and how these control signals are to be adjusted.

As represented by block 606 of FIG. 6, at least one of the fan control signals is adjusted based on the signals received at blocks 602 and 604. For example, in some cases, the signals received at block 602 are processed as described above at FIG. 5 to make an initial determination regarding whether and how to adjust the control signals. In addition, such an algorithm may take into account the signals received at block 604 to further verify or quantify peak spreading.

As represented by block 608, in some cases, the adjustment of a control signal is limited based on one or more factors. For example, the fan speed of one or more fans will typically be limited to be within a defined rotational speed range depending on the temperature that is required at specified locations in the enclosure (e.g., at a processor or at an interior space). Thus, in some implementations, one or more of the frequency, phase, or some other parameter of the control signals is selected to meet a defined temperature profile. This limiting of the control signal adjustment is based, for example, on received temperature signals and, optionally, received fan speed signals.

The arrow from block 608 to block 602 indicates that the operations of FIG. 6 are typically repeated to dynamically adjust the control signals over time. For example, each time around the loop, one or more of the control signals may be adjusted according to an optimization algorithm (and optionally one or more control parameters).

FIG. 7 illustrates an example of a system 700 that employs an optimization algorithm to control spreading (e.g., to maintain spreading within a defined target value). In a typical implementation, a control circuit employs an optimization algorithm whereby information derived from transducer signals received over time is used to adjust the fan control signals over time, as needed. This optimization algorithm may be embodied, at least in part, in executable code that is executed by a processing system, in a state machine, or in some other suitable manner.

In the embodiment of FIG. 7, transducer signals received from one or more transducers (not shown) are subjected to analog-to-digital conversion 702 to generate transducer data 704. The transducer data 704 is subjected to signal processing 706 that generates an indication of the current spreading 708. For example, in some embodiments, the signal processing 706 employs an FFT algorithm that operates on the transducer data 704 to extract frequency spectrum information, identify a peak spread from the frequency spectrum information, and generate a numerical spreading value corresponding to the peak spread.

An optimization algorithm 710 generates fan speed control and fan phase control data based, at least in part, on the indication of the current spreading 708. To this end, the optimization algorithm may store one or more fan control and spreading values 712 in a memory device (not shown). The type of values stored and the manner in which these values are used depends on the type of optimization algorithm being used.

In some embodiments, the optimization algorithm 710 employs a brute force scheme to minimize spreading. For example, the value(s) used for the last adjustment made to the fan speed control and fan phase control values may be stored along with at least one prior spreading value that was used to determine the adjustment. The optimization algorithm 710 may then compare the indication of current spreading 708 (e.g., a new spreading value) to the stored prior spreading value(s) to determine whether the last adjustment resulted in a decrease or an increase in spreading. The optimization algorithm 710 then generates at least one new adjustment value based on this determination (e.g., it continues adjusting the control values in the same manner if spreading decreased, or it adjusts the control values in a different manner if spreading increased). Similar techniques may be employed in other types of optimization schemes (e.g., a scheme that employs a least mean square-based algorithm).

In some embodiments, the optimization algorithm 710 employs a lookup table or other similar information. This information may specify, for example, the control value(s) to be used for a given current spreading value. For example, a predefined mapping between fan control and spreading values 714 may be predetermined (e.g., based on simulations and/or empirical testing) and stored in a memory device (not shown). Upon determining the current spreading value (e.g., the indication of current spreading 708), the optimization algorithm 710 uses this spreading value to lookup the new fan control value(s) to be used based on the mapping. It should be appreciated that other information (e.g., the current fan control value(s)) is taken into account here in some embodiments.

As additional transducer signals are received over time, the optimization algorithm 710 determines whether the speed control and phase control values need to be adjusted. For example, if the indication of current spreading 708 calculated based on the latest transducer signals indicates that the spreading is within a target value, the optimization algorithm 710 may maintain the speed control and phase control values at their current levels. Conversely, if the indication of current spreading 708 calculated based on the latest transducer signals indicates that the spreading is not within a target value, the optimization algorithm 710 may adjust the speed control and phase control values in a manner that is expected to reduce the spreading (e.g., as discussed herein).

As mentioned above, the teachings herein may be employed in various types of computing systems. FIGS. 8 and 9 illustrate two additional examples of how a fan control system as taught herein may be deployed in a computing system.

In FIG. 8, an enclosure 802 for a circuit 804 (e.g., a graphics card) houses several fans 806 and 808. In addition, a fan controller 810 (e.g., comprising receiver, control, and driver circuitry) and a microphone 812 are deployed within the enclosure 802 for proving fan control as taught herein. It should be appreciated that the functionality of the fan controller 810 and/or the microphone 812 is incorporated into the circuit 804 in some implementations.

In the example of FIG. 8, the circuit 804 connects to a PCB 814 (e.g., a motherboard). The PCB 814 is typically installed within an enclosure that has one or more fans (not shown). Thus, in some cases, the fan control circuitry for the enclosure 802 cooperates with fan control circuitry for the larger PCB enclosure to control all of the fans in the combined system in a manner consistent with the teachings herein. In implementations that employ multiple enclosures such as the enclosure 802, the fan control circuitry for each enclosure may cooperate with one another (and, optionally, with fan control circuitry for the PCB 814) to control all of the fans in the combined system in a manner consistent with the teachings herein. In some implementations, a single controller is employed (e.g., on the PCB 814 or in the enclosure 802) whereby that controller receives signals from all of the transducers in the system (e.g., including the microphone 812) and generates control signals for all of the fans in the system (e.g., including the fans 806 and 808).

In FIG. 9 (e.g., a top view of a server rack for server cards), an enclosure 902 houses several circuit cards 904A-904G and several fans 906A-906G. A fan controller 908 (e.g., comprising receiver, control, and driver circuitry) and several microphones (represented by the microphones 910A and 910B) are deployed within the enclosure 902 for proving fan control as taught herein. The functionality of the fan controller 908 and/or the microphones 910 may be incorporated into one or more of the circuit cards 904 in some implementations.

It should be appreciated that various modifications may be incorporated into the disclosed embodiments based on the teachings herein. For example, different algorithms may be employed in other embodiments to adjust the operation of a fan based on received acoustic-related information. Also, different types of transducers and/or different combinations of transducers other than those specifically shown may be employed in other embodiments.

A computing system as taught herein may be used in a variety of applications. For example, such a computing system may comprise or be incorporated into a portable device, a computer graphics card, a videogame console, a printer, a personal computer, a computer server, a processing system (e.g., a CPU device), or some other apparatus that employs multiple fans.

It also should be appreciated that the various structures and functions described herein may be implemented in various ways and using a variety of apparatuses. For example, an apparatus (e.g., a device) including functionality as described herein may be implemented by various hardware components such a processor, a controller, a state machine, logic, or some combination of one or more of these components. In some aspects, an apparatus or any component of an apparatus may be configured to provide functionality as taught herein by, for example, manufacturing (e.g., fabricating) the apparatus or component so that it will provide the functionality, by programming the apparatus or component so that it will provide the functionality, or through the use of some other suitable means.

In some embodiments, code including instructions (e.g., software, firmware, middleware, etc.) may be executed on one or more processing devices to implement one or more of the described functions or components. The code and associated components (e.g., data structures and other components by the code or to execute the code) may be stored in an appropriate data memory that is readable by a processing device (e.g., commonly referred to as a computer-readable medium).

The recited order of the blocks in the processes disclosed herein should generally be considered to be an example of a suitable approach. Thus, operations associated with such blocks may be rearranged in some cases while remaining within the scope of the disclosure. Similarly, the accompanying method claims present operations in a sample order, and are not necessarily limited to the specific order presented.

The components and functions described herein may be connected or coupled in various ways. The manner in which this is done may depend, in part, on whether and how the components are separated from the other components. In some embodiments some of the connections or couplings represented by the lead lines in the drawings may be in an integrated circuit, on a circuit board, in a cable, implemented as discrete wires, or implemented in some other way.

The signals discussed herein may take various forms. For example, in some embodiments a signal may comprise electrical signals transmitted over a wire, light pulses transmitted through an optical medium such as an optical fiber or air, or RF waves transmitted through a medium such as air, etc. In addition, a plurality of signals may be collectively referred to as a signal herein. The signals discussed above also may take the form of data. For example, in some embodiments an application program may send a signal to another application program. Such a signal may be stored in a data memory.

Also, it should be understood that any reference to an element herein using a designation such as “first,” “second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations may be used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements may be employed there or that the first element must precede the second element in some manner. Also, unless stated otherwise a set of elements may comprise one or more elements. In addition, terminology of the form “at least one of A, B, or C” or “one or more of A, B, or C” or “at least one of the group consisting of A, B, and C” used in the description or the claims means “A or B or C or any combination of these elements.”

It should be appreciated that specific structural and functional details disclosed herein are merely representative and do not limit the scope of the disclosure. For example, based on the teachings herein one skilled in the art should appreciate that the various structural and functional details disclosed herein may be incorporated in an embodiment independently of any other structural or functional details. Thus, an apparatus may be implemented or a method practiced using any number of the structural or functional details set forth in any disclosed embodiment(s). Also, an apparatus may be implemented or a method practiced using other structural or functional details in addition to or other than the structural or functional details set forth in any disclosed embodiment(s).

In view of the above, it will be understood that various modifications may be made to the illustrated embodiments and other embodiments as taught herein, without departing from the scope thereof. Accordingly, the teachings herein are not limited to the particular embodiments or arrangements disclosed, but are rather intended to cover any changes, adaptations or modifications which are within the scope of the appended claims. 

1. A control apparatus for controlling a plurality of fans in an enclosure, comprising: a receiver circuit to receive signals representative of an acoustic signature due to interaction of the fans in the enclosure; and a control circuit to generate control signals based on the received signals, wherein the control signals control the fans to reduce spreading of at least one acoustic peak of the acoustic signature.
 2. The apparatus of claim 1, wherein the received signals are generated by at least one acoustic transducer in the enclosure.
 3. The apparatus of claim 2, wherein: the receiver circuit receives a series of other signals generated by the at least one acoustic transducer over time; the other signals are representative of other acoustic signatures due to other interactions of the fans; and the control circuit adjusts at least one of the control signals based on the received other signals.
 4. The apparatus of claim 3, wherein the other signals are received continuously.
 5. The apparatus of claim 1, wherein the received signals are generated by at least one microphone in the enclosure.
 6. The apparatus of claim 1, wherein the received signals are generated by at least one pressure transducer in the enclosure.
 7. The apparatus of claim 1, wherein: the generation of the control signals comprises generating frequency spectrum information based on the received signals; and the frequency spectrum information represents the acoustic signature.
 8. The apparatus of claim 7, wherein the at least one acoustic peak of the acoustic signature comprises a peak of the frequency spectrum information, and wherein the generation of the control signals comprises: identifying a spread of the peak of the frequency spectrum information; and adjusting at least one of the control signals to reduce the spread of the peak of the frequency spectrum information.
 9. The apparatus of claim 1, wherein: the fans induce air flows in the enclosure; rotational speeds of the fans are modulated due to interaction of the air flows with the fans, thereby causing the spreading; and the control signals change the rotational speeds of the fans to reduce the modulation.
 10. The apparatus of claim 1, wherein: the fans induce air flows in the enclosure; rotational speeds of the fans are modulated due to interaction of the air flows with the fans, thereby causing the spreading; and the control signals change at least one relative phase between at least two of the fans to reduce the modulation.
 11. The apparatus of claim 1, further comprising a second receiver circuit to receive other signals indicative of temperature in the enclosure, wherein the generation of the control signals is further based on the received other signals.
 12. The apparatus of claim 1, further comprising a second receiver circuit to receive other signals indicative of rotational speeds of the fans, wherein the generation of the control signals is further based on the received other signals.
 13. The apparatus of claim 12, wherein the generation of the control signals limits the rotational speeds of the fans to be within at least one defined range of rotational speeds.
 14. The apparatus of claim 1, further comprising a second receiver circuit to receive other signals relating to operation of the fans, wherein the generation of the control signals is further based on the received other signals.
 15. The apparatus of claim 14, wherein the other signals relating to the operation of the fans comprise at least one of the group consisting of: signals indicative of power supplied to the fans, signals indicative of current supplied to the fans, and signals indicative of voltage supplied to the fans.
 16. The apparatus of claim 1, wherein the acoustic signature comprises fan blade passing noise.
 17. The apparatus of claim 1, wherein the acoustic signature comprises noise resulting from interactions of air flows induced by the fans.
 18. The apparatus of claim 1, wherein the enclosure comprises a housing for a computing system.
 19. The apparatus of claim 1, wherein the enclosure comprises: a housing for the fans, a housing for a personal computer, or a housing for a computer server.
 20. The apparatus of claim 1, wherein the control circuit employs an optimization algorithm that uses information derived from the received signals to maintain the spreading within a defined target value.
 21. The apparatus of claim 1, wherein the apparatus comprises an integrated circuit.
 22. A method for controlling a plurality of fans in an enclosure, comprising: receiving signals representative of an acoustic signature due to interaction of the fans in the enclosure; and generating control signals based on the received signals, wherein the control signals control the fans to reduce spreading of at least one acoustic peak of the acoustic signature.
 23. The method of claim 22, wherein the received signals are generated by at least one acoustic transducer in the enclosure.
 24. The method of claim 23, further comprising: receiving a series of other signals generated by the at least one acoustic transducer over time, wherein the other signals are representative of other acoustic signatures due to other interactions of the fans; and adjusting at least one of the control signals based on the received other signals.
 25. The method of claim 24, wherein the other signals are received continuously.
 26. The method of claim 22, wherein the received signals are generated by at least one microphone in the enclosure.
 27. The method of claim 22, wherein the received signals are generated by at least one pressure transducer in the enclosure.
 28. The method of claim 22, wherein: the generation of the control signals comprises generating frequency spectrum information based on the received signals; and the frequency spectrum information represents the acoustic signature.
 29. The method of claim 28, wherein the at least one acoustic peak of the acoustic signature comprises a peak of the frequency spectrum information, and wherein the generation of the control signals comprises: identifying a spread of the peak of the frequency spectrum information; and adjusting at least one of the control signals to reduce the spread of the peak of the frequency spectrum information.
 30. The method of claim 22, wherein: the fans induce air flows in the enclosure; rotational speeds of the fans are modulated due to interaction of the air flows with the fans, thereby causing the spreading; and the control signals change the rotational speeds of the fans to reduce the modulation.
 31. The method of claim 22, wherein: the fans induce air flows in the enclosure; rotational speeds of the fans are modulated due to interaction of the air flows with the fans, thereby causing the spreading; and the control signals change at least one relative phase between at least two of the fans to reduce the modulation.
 32. The method of claim 22, further comprising receiving other signals indicative of temperature in the enclosure, wherein the generation of the control signals is further based on the received other signals.
 33. The method of claim 22, further comprising receiving other signals indicative of rotational speeds of the fans, wherein the generation of the control signals is further based on the received other signals.
 34. The method of claim 33, wherein the generation of the control signals limits the rotational speeds of the fans to be within at least one defined range of rotational speeds.
 35. The method of claim 22, further comprising receiving other signals relating to operation of the fans, wherein the generation of the control signals is further based on the received other signals.
 36. The method of claim 35, wherein the other signals relating to the operation of the fans comprise at least one of the group consisting of: signals indicative of power supplied to the fans, signals indicative of current supplied to the fans, and signals indicative of voltage supplied to the fans.
 37. The method of claim 22, wherein the acoustic signature comprises fan blade passing noise.
 38. The method of claim 22, wherein the acoustic signature comprises noise resulting from interactions of air flows induced by the fans.
 39. The method of claim 22, wherein the enclosure comprises a housing for a computing system.
 40. The method of claim 22, wherein the enclosure comprises: a housing for the fans, a housing for a personal computer, or a housing for a computer server.
 41. The method of claim 22, wherein the generation of the control signals comprises employing an optimization algorithm that uses information derived from the received signals to maintain the spreading within a defined target value.
 42. A control apparatus for controlling a plurality of fans in an enclosure, comprising: means for receiving signals representative of an acoustic signature due to interaction of the fans in the enclosure; and means for generating control signals based on the received signals, wherein the control signals control the fans to reduce spreading of at least one acoustic peak of the acoustic signature.
 43. A control system for a plurality of fans in an enclosure, comprising: at least one transducer to generate signals representative of an acoustic signature due to interaction of the fans in the enclosure; a receiver circuit to receive the signals from the at least one transducer; and a control circuit to generate control signals based on the received signals, wherein the control signals control the fans to reduce spreading of at least one acoustic peak of the acoustic signature.
 44. A computer-program product for controlling a plurality of fans in an enclosure, comprising: computer-readable medium comprising code for causing a computer to: receive signals representative of an acoustic signature due to interaction of the fans in the enclosure; and generate control signals based on the received signals, wherein the control signals control the fans to reduce spreading of at least one acoustic peak of the acoustic signature. 